ABSTRACT
The production of a narrow, heavy, occasionally convective
snowband that fell within a modest surface cyclone on 19 January
1995 is examined using gridded model output from a successful num-
erical simulation performed using the University of
Wisconsin Nonhydrostatic Modeling System (UW-NMS). It is found that
the snowband was produced by a thermally direct vertical circulation
forced by significant lower tropospheric warm frontogenesis in the
presence of across-front effective static stability differences as
measured in terms of the equivalent potential vorticity (PVe).
The sometimes convective nature of the snowband resulted from the
development of upright, freely convective motions forced by frontal
lifting of the environmental stratification.
Model trajectories demonstrate that a stream of warm, moist
air ascended through the trowal portion of the warm occluded structure
that developed during the cyclone life cycle. The lifting of air in
the trowal was, in this case, forced by frontogenesis occuring in the
warm frontal portion of the warm occlusion. This trowal airstream
accounts for the production of the so-called "wrap around" precip-
itation often associated with occluded cyclones and, in this case,
accounted for the northern third of the heavy snowband.